1. Field
The present invention generally relates to endoscopes, and more particularly to an endoscope of the type referred to in claim 1.
2. Prior Art
Endoscopes of this type have an elongated shaft intended for introduction into the body to be examined, which consists essentially of two metal tubes, the outer shaft tube, which forms the stable and sealing outer wall of the shaft, and the fibre tube, which is located on the inside and delimits the free cross-section intended to accommodate the fibres of the optical fibre bundle toward the inside, thus with respect to the image guide.
A design of this class is disclosed in DE 10 2007 002 042 B4. In the usual design, the image guide is round. It consists, for example, of the round lenses of a set of relay lenses or an image guide fibre bundle with a round cross-section. Correspondingly, the fibre tube is also round. The free cross-section between the two tubes has the usual half-moon-shaped cross-section.
The image guide with its distally positioned objective must be accommodated in the round cross-section of the fibre tube, which is unproblematic in the case of the usual rotationally symmetric design of image guides. More and more often, however, endoscopes with two viewing directions are being designed, as is shown for example by DE 10 2009 020 262 A1. In this way, it is possible to look, for example alternately, in the straight-ahead direction and a direction at an angle to this. In this case the image guide can remain round essentially over its length. In the distal end region, thus in the area of the objective, widening of the cross-section in the direction of the objective section is necessary for the oblique viewing direction. This leads to design problems. The invention can also be used in an endoscope with a continuously adjustable viewing direction, as is known from DE 10 2009 049 843 B3.
If one attempts to place this distal cross-sectional widening in a round fibre tube, the latter must be enlarged. This leads to a substantial narrowing of the free cross-section and thus to a decrease in the number of optical fibres. The light transmission deteriorates, and the image becomes darker. In addition, the half-moon-shaped free cross-section between the two tubes presents a number of drawbacks with regard to accommodating the optical fibre bundle. For example, it limits the possibilities for the distal arrangement of the radiating surface of the optical fibre bundle.